Quadruple-label experiments have been performed in the human forearm (with insulin clamped at different levels) and myocardium (in different heart working conditions). An intravascular, extracellular, permeant nonmetabolizable and permeant metabolizable glucose tracers were used. The aim of these studies is to assess the extent to which glucose transport and metabolism in vivo are influenced in the forearm by different levels of insulin and in the myocardium by different heart beating rates. Experimental results will be analyzed using the compartmental and distributed approach. While this work progresses, additional knowledge about the physiology of these organs (e.g. flow heterogeneity in man) will be appropriately gathered and used in the modeling. Specific Aims: 1. To develop a mathematical model of capillary-tissue exchange suitable for analysis of the experimental results; 2. To determine the transport and metabolism of glucose in human muscle tissue, and its control by insulin, using the multiple indicator dilution technique.